The use of multilayer compositions for containers. such as bottles, jars and the like, and as packaging materials for storing food, beverages, and other perishable items has been known for quite some time. The concept of a multilayer structure is that the positive properties of two or more materials are combined with the structural integrity of each material being essentially uncompromised. Usually the advantageous and positive properties of one material off-set or counter-balance the weaker properties of the second material. Thus, for example, polycarbonate resins exhibit advantageous properties of excellent impact strength and heat resistance. However, polycarbonate resins generally exhibit relatively high permiability rates to water vapor and gas, such as oxygen and carbon dioxide, transport. On the other hand, there are known and available other polymeric materials which exhibit relatively good resistance to the transmission of water vapor. Still other known polymeric materials exhibit good resistance to the transport of gases such as oxygen and carbon dioxide. However these types of resins generally exhibit relatively poor resistance to impact and heat. Therefore, a multilayered structure can be hypothesized utilizing a polycarbonate resin layer in combination with one or more layers comprised of a polymeric material which is resistant to water vapor and/or gas transport. Such a structure should exhibit resistance to impact and heat as well as resistance to water vapor and/or gas transport.
Although such a multilayered structure can be hypothesized on the basis of laminating a material possessing certain strong properties with a material exhibiting weaknesses in those same properties, certain practical considerations inhibit implementation of this theory. The materials in the proposed laminar structure are in intimate contact at their interface. This juncture or interface should provide a sufficiently strong interaction with respect to the processing conditions which the multilayered structure undergoes so that a tight, firm and durable bond is maintained. Such conditions to which the multilayered structure can be exposed include heat, pressure, humidity, liquid chemicals, gasses and the like, or various combinations of these conditions. The propensity of the various layers to maintain this tight, firm and durable bond is generally known as the "compatibility" of these layers. When materials are incompatible the utility of the multilayer structure is severely inhibited or useless.
Aromatic polycarbonate resins are particularly useful for multilayer technology because of their high heat resistance, impact resistance, and clarity. However, polycarbonate resins are generally incompatible to varying degrees with a number of other resins.
It is an object of the instant invention to provide a multilayered structure which exhibits good resistance to impact and heat, resists water vapor transmission and gas transport, and in which the various layers or laminae maintain a tight, firm and durable bond.